cách nào nhanh nhất để nhận biết khí oxi?

Độ tan của NaCl ở 90oC là 50g và ở 0oC là 35g. Tính lượng NaCl kết tinh khi làm lạnh 900g dung dịch NaCl bão hòa ở 90oC.

Giúp mình bài này với !! Mình cảm ơn nhiều ☺️

Câu1: Bằng phương pháp hóa học hãy trình bày cách nhận biết các dung dịch sau: a) HCl, NaOH, Na2SO4, NaCl b) HCl, H2SO4, NaCl, Na2CO3 c) NaOH, BaCl2, Ba(OH)2, NaCl d) Na2SO4, K2CO3, BaCl2, AgNO3 e) KNO3, Cu(NO3)2, AgNO3, Fe(NO3)3 Câu2: bằng phương pháp hóa học hãy trình bày cách nhận biết các chất khí sau: a) CO, CO2, SO2 b) CO, CO2, SO2, SO3, H2 Bạn nào thông minh giúp mình với

Mọi người làm giúp em với ạ khó quá e k biết làm kiểu gì ạ em xin cảm ơn !!!

Làm hộ mình từ câu 5 đầu tiên đến hết phần II ạ.Tks😊

Bài 2: Tìm tham số m để hệ phương trình { mx + y = 5 có nghiệm duy nhất? 4x + 3y = 1 Hướng dẫn: Cách 1: Sử dụng điều kiện về nghiệm của hệ phương trình dựa vào các hệ số của chúng. Cách 2: Sử dụng các bước giải hệ phương trình bằng phương pháp thế. Rút ẩn y từ phương trình mx + y = 5, ta được y = –mx + 5 rồi thay vào phương trình còn lại. Để hệ phương trình có nghiệm duy nhất thì phương trình bậc nhất một ẩn vừa tìm được phải có nghiệm duy nhất, từ đó tìm m.

Điềm vào chỗ trống giúp mình với ạ

25 Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions. Many people now think that teachers give pupils too much homework. They say that it is unnecessary for children to work at home in their free time. Moreover, they argue that most teachers do not properly plan the homework tasks they give to pupils. The result is that pupils have to repeat tasks, which they have already done at school. Recently many parents complained about the difficult homework which teachers gave to their children. The Greek parents said that most of the homework was a waste of time, and they wanted to stop it. Spain and Turkey are two countries, which stopped homework recently. In Denmark, West Germany and several other countries in Europe, teachers cannot set homework at weekends. In Holland, teachers allow pupils to stay at school to do their homework. The children are free to help one another. Similar arrangements also exist in some British schools. Most people agree that homework is unfair. A pupil who can do his homework in a quiet and comfortable room is in a much better position than a pupil who does his homework in a small, noisy room with the television on. Some parents help their children with their homework. Other parents take no interest at all in their children’s homework. It is important, however, that teachers talk to parents about homework. A teacher suggests suitable tasks for parents to do with their children. Parents are often better at teaching their own children. Homework is unfair because _____. A: Some pupils have to help their parents with housework and some others do not B: Some parents help their children with their homework while some others do not C: Some pupils do their homework in a quiet and comfortable room while some others do homework in a small, noisy room D: A&B 26 Mark letter A, B, C or D on your answer sheet to indicate the sentence that is closest in meaning to the original sentence in each of the following questions. No one has asked me that question before. A: I have ever been asked that question before. B: That question has never been asked me before by anyone. C: That question has ever been asked me by no one before. D: I have never been asked that question before. 27 Mark the letter A, B, C or D on your answer sheet to indicate the meaningful sentence from the cues given. Children / should have / special day / express / feeling / memories / /love/their parents. A: Children should have a special day expressing their feeling, memories and love to their parents. B: Children should have a special day express their feeling, memories and love for their parents. C: Children should have a special day to express their feeling, memories and love for their parents. D: Children should have a special day expressing their feeling, memories and love for their parents. 28 Mark the letter A, B, C or D on your answer sheet to indicate the meaningful sentence from the cues given. The novels / I / just / read / interesting. A: The novels who I have just read are interesting B: The novels whom I have just read is interesting C: The novels which I had just read is interesting D: The novels which I have just read are interesting. 29 Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions. Watching TV all day is a bad habit _____ we get no exercise and eat unhealthy snacks. A: therefore B: though C: because D: but 30 Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions. The ones about ______ I have been worried these days are the students of mine. A: which B: whom C: that D: whose 31 Mark the letter A, B, C or D on your answer sheet to indicate the word that differs from the other three in the position of primary stress in each of the following questions. \ A: escape B: control C: mention D: replace 32 Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks. Japan, (23) ______on the Ring of Fire on the edge of the Pacific Ocean, has suffered some major earthquakes over the years. However, nothing before compared to the triple disaster of March 11, 2011: a massive earthquake followed by powerful tsunamis (24)_____ led to a serious nuclear accident. The horrors began shortly before three (25)___ the afternoon local time with a 9.0-magnitude earthquake. Its epicenter was nearly 20 miles (26)___the floor of the Pacific Ocean, about 80 miles east of the Japanese city of Sendai. The quake was one of the most powerful ever recorded and the (27)_______ to hit this region of Japan. Question 25. A: in B: over C: on D: at

Bài 3. Cho tam giác ABC, các đường cao BD và CE cắt nhau tại H. Chứng minh rằng: a) AE.AB = AD.AC. b) BEH ∽ CDH. c) EHD ∽ BHC. d) BC^2= BH.BD + CH.CE